This invention relates in general to imaging devices used to detect breast cancer and more particularly to such imaging devices known as transillumination devices which use non-ionizing radiation such as optical radiation to image the interior of the breast.
Transillumination imaging devices and methods (sometimes referred to as xe2x80x9coptical mammographyxe2x80x9d) for diagnosis of breast lesions were first described in an article by Cutler in the Journal of Surgical Gynecology, Obstetrics Vol., 48:721 (1929). Transillumination imaging uses intensive non-ionizing radiation such as light that is detected after transmission through the breast and processed to provide image data from the interior of the breast.
The main motivating factor behind the use of transillumination for detection of breast cancer rather than x-rays has been the problems caused by the ionizing x-rays. For safety reasons it is recommended that the use of x-rays for detection of cancer generally be restricted to women age 40 and over and further be restricted to only one test per year. The use of non-ionizing radiation devices such as ultrasound or transillumination enables testing women under 40 as well as over 40 and is not restricted to use once per year. There are no negative safety repercussions derived from testing for breast cancer more than once a year using non-ionizing radiation.
U.S. Pat. No. 4,945,239 describes prior art transillumination devices and the problems inherent with such devices. An important problem with transillumination devices is that the low energy photons of the light beams are easily scattered and therefore produce blurred images. The transillumination prior art used many methods in attempting to reduce the scatter and to generally improve the transillumination images. However, the scatter reducing methods and devices described by the prior art are relatively complicated and difficult to use. For example, the aforementioned patent describes reducing scatter by using a pin hole box between the light source and the breast and again between the breast and the detector. This does reduce scatter, however, the pin hole boxes and light sources have to be very accurately aligned and even more detrimental is the fact that the procedure is time consuming because the pin hole boxes are used in a scanning regimen to image the breast interior.
U.S. Pat. No. 4,945,239 also describes using an unspecified marker that is opaque to an unspecified wavelength of light as a contrast agent
Another method of reducing scatter is through the use of complicated optical lens systems or polarizing filters between the light source and the breast and between the breast and the detector.
Yet another prior art scatter reducing procedure uses mirrors. A semi-permeable mirror is used between the light source and the breast to transport light to the breast and to a detector in conjunction with a phase conjugated mirror that receives light that has traversed the breast. The phase conjugated mirror sends the light back through the breast to the semi-permeable mirror and the detector. Thus, the prior art faced the problem of light scattering when transillumination was used to detect cancer in breasts by providing complicated systems such as complicated lens systems, mirror systems and pin hole systems.
The great difficulty in discovering lesions embedded in breast tissue by transillumination was highlighted in a theoretical investigation by Navarro et al. described in the Medical Physics Journal 15:181 (1988). That study concluded that lesions of 0.5 centimeter in size would not be detected by transillumination if located deeper than 0.5 centimeters from the skin surface because of scatter caused by the skin surface interface.
A prior art system used xe2x80x9ctime of flightxe2x80x9d analysis to distinguish light beams traversing the breast in a straight line from the source to the detector from scattered light.
In the patents listed and analyzed in the above mentioned patent it seems that only U.S. Pat. No. 4,767,928 discloses obtaining planar or tomographic images. The planar image is obtained by rotating the light beams around the breast. The prior art does not acquire images by focusing on different planes illuminated by the light traversing the breast. The patents in general merely examine the light that makes it through the breast and does the imaging based strictly on the intensity of light traveling through the breast detected after traveling through the breast wherein the intensity of the light is used to obtain mainly shadowgraph images based on absorption and scatter. Thus the detected light is light that was not absorbed by the tissue is imaged. Where absorption is high; then the cause of the high absorption is attributed to a possible lesion. Thus if a lesion exists at some level in the breast the detection of the lesion is hampered by scatter and by variations in the overlying and underlying structure of the breast all of which are imaged together.
More recently in transillumination apparatus, broad beam light sources referred to as xe2x80x9clight torchesxe2x80x9d have been used for breast imaging.
Again, the main problem is scatter. Spatial resolution and contrast are lost because of scatter. U.S. Pat. No. 4,948,974 acquires image data by focusing the light coming into the breast onto points in the breast and then moving the light source to scan different planar sections within the breast and to detect the light from those planes. This patent mentions the use of single wavelength illumination to reduce scatter, in contrast to the prior art which uses broadband illumination.
UK patent GB 2 111 794 inter alia describes a system in which a breast is illuminated by a collimated beam as from a projector or from a laser and an expander. Light passing through the breast is detected by either a contact detector or by a television camera. However, since collimated light is used for illumination, both detection methods provide only a shadowgraph of the breast.
In summary, the prior art may be divided into two broad categories. A first category of prior art systems images shadowgraphs of the breast without substantial specificity as to the depth. The second category focuses beams on a point in the breast and requires scanning to image the breast.
In general methods of detecting cancer in the breast using transillumination, use red visible light and/or infrared light, generally to detect patterns of increased vascularity which surrounds breast cancer. It is believed that such light is used because light (other than red) in the visible range is strongly attenuated by body tissues (especially by the blood).
The present invention is directed to non-ionizing radiation imaging system especially useful for mammography.
One aspect of some preferred embodiments of the invention provides for imaging of planes of the breast utilizing non-ionizing radiation. The advantages of this aspect of the invention is that it significantly reduces the effects of overlying and underlying structures in selectively imaging a plane of the breast, rather than imaging a shadowgraph. This is facilitated through the use of a special contact window primarily located between radiation detectors and tissue being imaged and by the use of a camera focused on a depth of a slice to be imaged.
In addition, in accordance with an aspect of some preferred embodiments of the invention, light in ranges other than red is used to image the breast. In particular, light of various limited ranges of wavelengths is used to selectively image the breast. The limitation takes advantage of the fact that different anatomical structures absorb different wave lengths of light energy to different extents. Breasts consist in large proportion of fatty tissue. The range of wave lengths used, i.e. 490-670 nanometers is centered around the wave length of minimal optical absorbency of the fatty tissue in order to assure sufficient light transmission for detection. In this wave length range the absorbency differences, i.e., the contrast between the different tissue types is much higher than it is in the infrared region used extensively in the prior art. Successful imaging in this wave length region, is surprising since the overall transparency in that region is very low. However, it has been found that despite the fact that only a low light intensity comes through, nonetheless cross sectional images with clearly recognizable anatomical details are obtained because of the relatively high contrasts. The details are improved when using the special contact window to reduce to a large extent interfering light scattering of the tissue at the skin to air interface.
In preferred embodiments of the invention the detector focuses on different planes of the breast per imaging scan. Each of the planes are then preferably imaged, using different wave lengths of light, to provide increased diagnostic information.
In a further preferred embodiment of the invention, stereoscopic imaging, utilizing one or both of the above aspects of the invention is provided. This is accomplished by obtaining multiple images of the same plane observed from different angles.
There is thus provided, in accordance with a preferred embodiment of the invention, apparatus for imaging cross sectional views of the inner structure of the breast, the apparatus comprising:
a source of light, illuminating the breast, situated at a first position of the breast;
a matching interface situated, at a second position, on a surface of the breast, which reduces scatter caused by said surface; and
an imaging detector focused on a plane within the breast, through said matching interface.
Preferably, is configured with lenses to provide a selectable plane in the breast to be imaged on the detector. Preferably, the lenses provide a narrow depth of field.
In a preferred embodiment of the invention, the matching interface comprises a surface of a transparent non-porous material and the breast.
Preferably, the imaging detector comprises one or more of a matrix detector, a video camera, a CCD array and a photographic film.
In a preferred embodiment of the invention the apparatus includes an optical filter situated between the source and the detector that limits the light reaching the detector from the source to a visible spectral band excluding red.
There is further provided, in accordance with a preferred embodiment of the invention apparatus for imaging of the inner structure of the breast, the apparatus comprising:
a source of light illuminating the breast situated at a first position of the breast;
a detector situated at a second position relative to the breast, said detector detecting light from said source passing through a portion of the breast from the source; and
an optical filter situated between source and the detector that limits the light reaching the detector from the source to a visible spectral band excluding red.
Preferably, the optical filter has a lower pass-band limit of 520 nanometers or more and an upper pass-band limit of 580 nanometers or less. Alternatively the optical filter has a lower pass-band limit of 490 nanometers or more and an upper band-pass limit of 510 nanometers or less.
In a preferred embodiment of the invention, the apparatus includes:
a plurality of optical filters;
a filter holder situated between the source and the detector, such that when a filter is placed in said holder light reaching the detector from the source is limited to a visible spectral band different from that of at least one of the other filters and wherein at least one of the filters transmits in a range outside the red and infra-red; and
means for selectively changing the filter in the holder.
There is further provided, in accordance with a preferred embodiment of the invention apparatus for imaging of the inner structure of the breast, the apparatus comprising:
a source of light illuminating the breast situated at a first position of the breast;
a detector situated at a second position relative to the breast, said detector detecting light from said source passing through a portion of the breast from the source;
a plurality of optical filters;
a filter holder situated between the source and the detector, such that when a filter is placed in said holder light reaching the detector from the source is limited to a visible spectral band different from that of at least one of the other filters and wherein at least one of the filters transmits in a visible range outside the red and infra-red; and
means for selectively changing the filter in the holder.
In a preferred embodiment of the invention, at least one of the filters has a lower pass-band limit of 520 nanometers or more and an upper pass-band limit of 580 nanometers or less.
In a preferred embodiment of the invention, at least one of the filters has a lower pass-band limit of 490 nanometers or more and an upper pass-band limit of 510 nanometers or less.
In a preferred embodiment of the invention, at least one of the filters has a lower pass band limit greater than 620 nanometers.
In a preferred embodiment of the invention the source of light comprises an incandescent light source. Alternatively or additionally the source of light comprises a high intensity discharge light source.
In a preferred embodiment of the invention, the source of light is a laser source having an output in the visible spectral band excluding red.
There is further provided, in accordance with a preferred embodiment of the invention, apparatus for imaging of the inner structure of the breast, the apparatus comprising:
a source of laser light having an output in the visible spectral band excluding red illuminating the breast situated at a first position of the breast; and
a detector situated at a second position relative to the breast, said detector detecting light from said source passing through a portion of the breast from the source.
In a preferred embodiment of the invention, the source of laser light has an output at between 490 and 510 nanometers. Alternatively or additionally, the source of laser light has an output at between 520 and 580 nanometers. Alternatively, the laser source provides a tunable laser output. Preferably, the laser is tunable to a wavelength above 620 nanometers.
There is further provided, in accordance with a preferred embodiment of the invention, apparatus for obtaining stereotactic images of the interior of a breast, comprising:
at least one source of light illuminating the breast and situated at a first position of the breast;
at least one matching interface situated, at a second position, on a surface of the breast, which reduces scatter caused by said surface; and
a pair of spaced imaging detectors that view a portion of the breast through said at least one interface and produce images of said portion;
means for viewing the images such that a sterotactic image is perceived by a viewer.
Preferably, the apparatus includes an optical arrangement for focusing each of the detectors on a same region in the interior of the breast.
Preferably, the matching interface comprises a surface of a transparent non-porous material and the breast.
In various preferred embodiments of the invention the imaging detectors comprise one or more of matrix detectors, video cameras, CCD arrays and photographic film.
In a preferred embodiment of the invention, the apparatus includes a breast cage for supporting the breast during imaging.
There is further provided, in accordance with a preferred embodiment of the invention, a method of imaging the breast comprising:
illuminating the breast;
reducing interface light scatter generation at a portion of the surface of the breast; and
selectively imaging a slice in the breast through the portion.
In a preferred embodiment of the invention, the method includes imaging a plurality of slices within the breast. Preferably, imaging a plurality of slices comprises imaging slices at angles to each other. Alternatively or additionally, imaging slices comprises imaging slices from different vantage points outside the breast.
In a preferred embodiment of the invention the method includes producing a three dimensional image from said multiple images.
In a preferred embodiment of the invention, the method includes correcting one of said images based on at least a second one of said images. In various preferred embodiments of the invention correcting comprises one or more of correcting for background and scattered light, and correcting for unfocused light from overlying and underlying structures.
In a preferred embodiment of the invention, correcting comprises:
imaging a slice from two slightly different vantage points; and
reducing the effects of scatter from one of the images based on the other of the images.
In a preferred embodiment of the invention the method includes limiting the light used for imaging to a visible spectral band excluding red.
There is further provided, in accordance with a preferred embodiment of the invention, a method of imaging the breast comprising:
illuminating the breast;
forming an image of said illumination passing through a portion of the breast; and
limiting the light used for imaging to a visible spectral band excluding red.
In a preferred embodiment of the invention, the visible spectral band is limited to a band having a lower band limit of at least 520 nanometers and an upper band limit of below 580 nanometers. Alternatively, the visible spectral band is limited to a band having a lower band limit of at least 490 nanometers and an upper band limit of below 510 nanometers.
In a preferred embodiment of the invention, the method includes separately imaging the breast at a plurality of wavelengths or wavelength bands, at least one of which encompasses a range outside the red and infra-red.
There is further provided, in accordance with a preferred embodiment of the invention, a method of imaging the breast comprising:
illuminating the breast; and
separately imaging the breast at a plurality of wavelengths or wavelength bands, at least one of which encompasses a range outside the red and infra-red.
In a preferred embodiment of the invention at least one of the images is generated from light having wavelengths between 520 nanometers and 580 nanometers.
In a preferred embodiment of the invention at least one of the images is generated from light having wavelengths between 490 nanometers and 510 nanometers.
In a preferred embodiment of the invention at least one of the images is generated from light having a wavelength greater than 620 nanometers.
In a preferred embodiment of the invention, the method includes utilizing wavelengths of light in producing images such that larger blood vessels are emphasized. Alternatively or additionally, the method includes utilizing wavelengths of light in producing images such that fine blood vessels are emphasized. Alternatively or additionally the method includes utilizing wavelengths of light in producing images such that tumor tissue is emphasized.